Provided is a positive active material for a lithium secondary battery containing a lithium transition metal composite oxide. The lithium transition metal composite oxide has an α-NaFeO2 structure. A transition metal (Me) includes Co, Ni and Mn and a molar ratio Li/Me of lithium (Li) to the transition metal is larger than 1.2 and smaller than 1.6. The lithium transition metal composite oxide has a pore volume of 0.055 to 0.08 cc/g in a pore region in which a pore size, at which a differential pore volume determined by a BJH method from an adsorption isotherm using a nitrogen gas adsorption method exhibits a maximum value, is within a range up to 60 nm, and exhibits a single phase belonging to a space group R3-m at 1000° C.